test.sql

SELECT
  spree_orders.id
FROM
  spree_orders
WHERE (
  spree_orders.id IN (
    SELECT order_id
    FROM spree_orders_promotions
    INNER JOIN
      spree_promotion_codes
      ON spree_promotion_codes.id = spree_orders_promotions.promotion_code_id
    WHERE spree_promotion_codes.value LIKE '%first15%'
  )
  AND spree_orders.completed_at IS NOT NULL
)